People have saved and shared photographs since the commercialization of film photography. Although digital cameras have almost completely supplanted film cameras, people still often desire hand held photographs. Many people simply print their photographs on color printers whereas others purchase more specialized photo-printers that can produce a higher quality product. Another solution that has proven popular is the photo kiosk. A photo kiosk provides a photographer with access to high quality printing equipment that is outside the budgetary capability of most people. A photographer can, for a fee, submit image descriptions such as jpeg files to the kiosk and select printing options such as size, media, and finishing. The kiosk then prints out the photographer's images.
Digital watermarks provide for the authentication or tracking of documents. For example, American currency carries a watermark that can be observed under the correct viewing conditions. The water mark helps prevent counterfeiting because it represents a technological hurdle for counterfeiters. As such, the watermark helps authenticate the currency. Other types of digital watermarks have been developed. Glossmarks and correlation marks are examples of newer digital watermarks.
Glossmarks, also known as reflectivity marks, are taught in U.S. Pat. No. 6,108,512 “Copy prevention method”, U.S. Pat. No. 7,148,999 “Variable glossmark” and in U.S. Pat. No. 7,352,493 “Enhancement of glossmark images at low and high densities”. U.S. Pat. Nos. 6,108,512 and 7,148,999 teach printing glossmarks onto documents. Note that GlossMark is a registered trademark of Xerox corporation, and that Xerox Corporation owns U.S. Pat. Nos. 6,108,512, 7,148,999, and 7,352,493. Glossmarks are digital watermarks that are produced by printing patterns of reflectivity variation on the surface of a printed document or printed image. The reflectivity variations are most easily observed by tilting the page such that light is differentially reflected to the eye. U.S. Pat. No. 7,352,493 teaches ways to improve glossmark printing because glossmarks are more visible when printed over mid-tone document areas.
FIG. 7, labeled as “Prior Art”, illustrates the classification of pixels as a function of pixel value. An arrow 701 indicates the direction of increasing pixel values where higher pixel values indicate lighter pixels. Dark pixels 702 have lower pixel values and light pixels 704 have higher pixel values. Mid-tone pixels 703 have midrange pixel values. For example, the mid-tones can be the middle third or middle quartile of pixel values. The light tones can be the upper third or upper quartile of pixel values. The dark tones can be the lower third or lower quartile of pixel values.
One type of correlation mark is taught in U.S. Pat. No. 5,734,752 “Digital watermarking using stochastic screen patterns”. In essence, a correlation mark is a digital watermark that is invisible or hardly visible on a printed document or image but that becomes visible when the document is viewed through a correlation mask. A pattern printed onto a transparency is an example of a correlation mask. Aligning the correlation mask to the printed document or image causes a correlation image to become visible.
Many people desire the capability to use digital watermarks but lack access to the required specialized printers and also lack the required specialized skills. Systems and methods providing for the use of digital watermarks by non-expert users are needed.